Exemplary embodiments of the present invention relate to an integrated circuit (IC) design technology, and more particularly, to an impedance calibration mode control circuit for controlling a calibration operation on a resistance and an ODT (On-Die-Termination) value in response to PVT (Pressure, Voltage and Temperature) variations.
FIG. 1 is a diagram illustrating a conventional ZQ calibration control circuit.
In general, the ZQ calibration performs a pull-up calibration operation on an internal pull-up resistor coupled to an external termination resistor (RZQ) 8, and performs a pull-down calibration operation on an internal pull-down resistor coupled to an internal pull-up resistor according to the result of the pull-up calibration operation.
More specifically, as illustrated in FIG. 2, a pull-up calibration operation is performed using a PCODE<0:N> signal generated by a counter 3. When an external resistance RZQ and an internal pull-up resistance RUP become equal to each other by the pull-up calibration operation, a current IUP and a current IDN become equal to each other at a ZQ node and the potential of the ZQ node becomes ½ VDDQ.
As illustrated in FIG. 3, a pull-down calibration operation is performed using a PCODE<0:N>signal generated by a counter 3 and a NCODE<0:N>signal generated by a counter 5. The pull-down calibration operation equalizes a pull-down resistance RDN and a pull-up resistance RUP calibrated by the pull-up calibration operation. Thus, when the pull-up resistance RUP and the pull-down resistance RDN become equal to each other, a current IUP and a current IDN become equal to each other at a NCAL_DQ node and the potential of the NCAL_DQ node becomes ½ VDDQ.
In this manner, the potential of the ZQ node and the potential of the NCAL_DQ node are controlled to the target value ½ VDDQ in ZQ calibration control mode by the pull-up calibration operation control and the pull-down calibration operation control as illustrated in FIG. 4.
As illustrated in FIG. 6, the above-described ZQ calibration control mode includes: a ZQINIT mode (corresponding to tZQInit) performed first after a power up; a ZQOPER mode (corresponding to tZQOper) performed according to an input from a controller during the operation of a semiconductor device; and a ZQCS mode (corresponding to tZQCS) performed at periods of, for example, 128 ms. The ZQINIT mode and the ZQOPER mode are included in a ZQCL mode. Here, the ZQINIT mode may be performed within 512 cycles. The ZQOPER mode may be performed within 256 cycles. The ZQCS mode may be performed within 64 cycles.
As illustrated in FIGS. 5 and 7, the ZQ calibration control mode is performed according to a ZQ command generated in response to CS#, RAS#, CAS# and WE# signals. For example, the ZQCL mode is performed when an address signal A<10> is high logic level ‘1’; and the ZQCS mode is performed when the address signal A<10> is low logic state ‘0’.
As illustrated in FIG. 8, in the conventional ZQ calibration mode control, a power-up operation is performed when a ZQ command ZQC is inputted and an address signal A<10> is high logic level ‘1’. When the ZQ command is inputted first, a state signal INIT_STATE changes to a high state and a ZQINIT mode is performed. After the ZQINIT mode is performed, when the state signal INIT_STATE changes to a low state, the ZQ command ZQC is inputted and the address signal A<10> is high logic level ‘1’, a ZQOPER mode is performed and an calibration control operation is performed according to a ZQCL mode.
Here, as illustrated in FIG. 7, the conventional auto ZQ calibration circuit controlling a ZQ calibration operation as described above may not accommodate command control operations other than those described above for performing the calibration operations according to the ZQCL mode and the ZQCS mode, where a high impedance state Hiz as represented by a DQ data bus is maintained.
In performing the ZQCS mode operation at periods of 128 ms according to an example, some operations may not be performed at every ZQCS mode operation. A device for ensuring performance of all control operations the ZQCS mode operation at periods of 128 ms would be useful.